1. Field of the Invention
The invention relates to a magnetic write/read head and to methods for the fabrication of such a head. More particularly, the invention can be applied to the technique of read/write magnetic heads for the technically very advanced magnetic disks and/or tapes used in computer peripherals for writing and reading operations on magnetic tapes and disks. It could also be applied to other types of equipment such as tape recorders and video recorders.
2. Description of the Prior Art
At present, the rotating magnetic write/read heads use a "bulk" type of technology (that is, a non-integrated technology). This technology involves delicate steps for the polishing and bonding of the poles. The increase in the density of writing on the new media has made it necessary to have write heads that perform better.
To enable the writing of increasingly smaller pieces of information on magnetic tapes, the coercivity of these tapes has to be increased. In particular, to record a high definition digital video signal, it is estimated that the dimensions of the elementary bit will be close to 0.2 .mu.m (in the running direction of the tape) per 5 .mu.m (width of the track). The EM (evaporated metal) tape is presently the most promising candidate for achieving performance levels of this kind: its coercivity is close to 1000 oersteds.
Magnetic tapes too need to undergo development. In particular, the zone liable to be saturated, in the vicinity of the gap, should be constituted by a material with a level of magnetization at saturation that is far higher than that of the ferrites typically used (4.pi.Ms=5000 Gauss: empirically, it is known that, typically, seven times the coercivity of the tape, i.e. 7000 Gauss in this example, needs to be attained in the gap for accurate writing.
These requirements have complicated the technology used to make these components.
New structures of heads have therefore appeared in the market. Their main characteristics are given here below:
Metal-In-Gap (MIG) type heads in which the body is composed of an Mn-Zn ferrite with high permeability, and the poles are coated with a layer of sendust (an alloy of iron, aluminium and silicium). An intermediate magnetic "matching" layer is provided between each pole and the sendust layer that covers it so as to reduce the secondary gap phenomenon and preserve a sendust/ferrite interface parallel to the main gap. The technology used to make these components could have been simplified to the point of becoming very similar to the well-known technology of ferrite heads. The presence of a pseudo-gap at the interface between the sendust and the ferrite has made it necessary to modify the structure of this head and has given rise to the following heads.
TSS (tilted sputtered sendust) type heads which are far more sophisticated than the preceding ones. In these TSS heads, the main body of the head is made of ferrite, but the poles are constituted by a magnetic material with high magnetization at saturation (sendust: 44.pi.Ms: 12000 Gauss). The sendust/ferrite interface also behaves like a small-sized gap. It is therefore necessary to incline it with respect to the useful gap so that no destructive interference on the reading signal is obtained. This constraint leads to a very complicated fabrication technology, hence one that is very costly, and to output efficiency levels that are difficult to control.
MIG heads wherein the problem of the pseudo-gap is resolved by the interposition, between the sendust and the ferrite material, of a matching layer making it possible to prevent destructive interferences from affecting the reading signal.
However, these heads are limited in frequency (due to the ferrite body and the eddy current in the sendust), and their bulk type technology is ill-suited to narrow tracks.
Indeed, these above-mentioned structures are ill-suited to the high frequencies of the high-definition digital signals at which it is necessary to work:
the standard ferrite structure used has an excessively low cut-off frequency;
eddy currents develop in the sendust which is not sufficiently resistive, and its magnetic permeability falls sharply. The relative directions of the field and of the plane of deposition of these materials unfortunately does not allow for the lamination of the sendust in order to reduce the currents induced.
A third type of head, the laminated head, has therefore been recently designed:
LTFH (laminated thin film head): this head is constituted by a stack of thin films with high magnetization uncoupled from one another by one or more fine non-magnetic layers to prevent the eddy currents from developing. The total thickness of the stack defines the width of the track written on. The width of the gap is defined by the thickness of the non-magnetic layer between the two parts of the head.
The absence of a ferrite body and the deposition of magnetic layers that perform well in a plane parallel to the tracks written on, firstly, enables use at high frequency and, secondly, is well suited to narrow writing tracks. By contrast, the making of the gap by the same method as the "bulk" method eliminates this latter advantage and converts even this potential advantage of the thin layers into a major disadvantage. Indeed, especially for small track widths, it is very difficult to accurately align the two parts constituting such a head and, hence, to position the magnetic poles so that they face each other precisely. Finally, this technology requires a final individual processing (rounding) operation on the heads, and therefore entails a high fabrication cost.
The above-described technologies require a processing of the heads in strips, up to the final rounding of each head which is done first of all on a strip, and then head by head. Our proposal enables a batch processing operation (two-dimensional substrate) up to the final rounding operation.
The object of the present invention consists in resolving this problem and in making full use of the advantages related to the deposition of thin layers, these advantages being the batch procedure and the perfect matching with the narrow tracks. In particular, the invention enables an extremely precise automatic alignment of the magnetic poles. Besides, all the characteristics of the last type of structure presented are preserved.